1. Field of the Invention
This invention relates to a microscope using an oil immersion system objective for observing fluorescent light emanating from a sample, such as a living cell, and an observation method of this microscope.
2. Description of Related Art
In the most advanced research field at present, various methods of observing cells, in vivo, for a long period of time (several days to several weeks) are developed for purposes of the functional clarification of living cells and the behavior analysis and interaction clarification of a protein. As one technique of microscopy for observing a lesion part inside a living cell, a fluorescence observation has been generally carried out. The fluorescence observation is such that, after a particular fluorescent substance like a fluorescent protein is used as a light-emitting label to stain a living sample such as the living cell, fluorescent light is produced by irradiating the sample with exciting light and is observed to thereby detect the existence of a particular part in the living sample, such as the lesion part inside the living cell, and its position.
In an observation under a fluorescence microscope, there is a particular demand that an S/N ratio should be good. In order to detect faint fluorescent light, it is necessary to use an oil immersion system objective in which high-resolution and bright fluorescent light is obtained.
The fluorescence microscope using a conventional oil immersion system objective is set forth, for example, in Japanese Patent Kokai No. 2002-350734. Immersion oil for fluorescence microscopes is described, for example, in Japanese Patent Kokai No. Hei 11-269317.
In the fluorescence microscope using the oil immersion system objective, however, as described in Kokai No. Hei 11-269317, auto-fluorescence emanating from immersion oil charged between a sample (strictly speaking, a cover glass covering the sample) and the oil immersion system objective adversely affects the S/N ratio. Thus, in order to obtain a high S/N ratio, it is desired to minimize a distance between the sample and the oil immersion system objective.